Decorating a three-dimensional article via in-mold decoration (IMD) or insert mold decoration involves inserting a decorative film into a molding tool in combination with a molten base polymer during an injection molding cycle. The decorative film is then bonded with or encapsulated by the molten base polymer, after the injection molding cycle is complete, to obtain an injection molded article or finished part having the desired decoration. The decoration for the finished part can either be exposed to the environment as “first surface decoration” and/or encapsulated between the substrate of the decorative film and the injected material as “second surface decoration.” Thus, the decorative film becomes a permanent fixture of the finished part. The film can act as an aesthetic effect carrier and/or as a protective layer for the base polymer, the ink, or both. The term “decorative” or “decoration” herein refers to surface printing or marking of an aesthetic, functional and/or informational nature that is printed on the decorative film including, for example, symbols, logos, designs, colored regions, and/or alphanumeric characters.
The decorative film can be printed with ink, specifically formable and high temperature inks. The film can then be formed on a tool into a three-dimensional shape that corresponds to the three-dimensional shape desired for the injection molded article.
Such processes are disclosed in U.S. Pat. No. 6,117,384 to Laurin et al., which describes a process wherein a colored decorated film is incorporated with a molten resin injected behind the film to produce a permanently bonded three-dimensional piece. U.S. Pat. No. 6,458,913 to Honigfort and U.S. Pat. No. 6,682,805 to Lilly also describe insert mold decorative films and articles. Lilly describes a multi-layer thermoplastic printable film comprising a thermoplastic film substrate having laminated to one surface a fluoride polymer in order to improve the birefringence and other properties of the film, including chemical resistance.
Increasingly it is desired that the exposed surface of a decorative film be resistant to scratch, abrasion, and chemical attacks. A cost-effective method to improve the surface characteristics of the film is to coat the film with a coating that provides the desired performance properties. For example, SABIC Innovative Plastic's LEXAN™ HP92S polycarbonate is coated with a proprietary hard coat specifically to improve surface durability against scratch and abrasion. The hard coat forms a bonded layer on the surface of the film, typically from 3 to 18 micrometers. The coating layer, however, is more brittle than desirable and, therefore, can limit the ability of the hard-coated film to be shaped or embossed.
In one approach, a coated polycarbonate film is only partially cured during the initial phase of the film production. Partially curing the film allows the hard coat to remain soft and compliant during thermoforming to shape the film. After the film had been thermoformed and put through an IMD process, the resulting article is then exposed to ultraviolet (UV) light for post-curing to achieve the desired surface hardness. This approach has a number of drawbacks. The partially cured film can only be exposed to special lighting. Normal lighting has a UV component that can cause a premature curing of the partially cured film. The soft surface of the partially cured film is prone to damage while it is being processed through the printing, thermoforming, and in-mold decoration injection steps, leading to a high level of yield loss. It is desirable to have a film with a hard coat already cured so that the coated film is robust to handling and does not need special lighting requirements.
In an alternative approach, an IMD three-dimensional article could also be subjected to post-production coating and subsequent curing. However, this added step in the manufacturing process can be expensive, time consuming and not provide a level of coating control, uniformity, and quality comparable to that of a pre-coated film. Post-production coating and subsequent curing can also need to be specific for a particular article, and some articles, due to their size or geometry, can need special handling requirements. A pre-coated film would eliminate these drawbacks or problems.